Fluorescence analysis



AGENT 1960 l I. BESSEN FLUORESCENCE ANALYSIS Filed Aug. '9, 1956 ,Pt nt d eb.-

* United Swiss;

My invention relates to the quantitative analysis of materials for an elementor elementstherein and in particular relates to a method and apparatus for the nondestructive analysis of materials by X-rays.- I

Materials can be analyzed for an elementor elements therein by X-rays withoutdestroying the material. In thismethod, each element of the material is excited by primary X-radiation, usually generated by .an X-r'ay tube, into -producing its characteristic fluorescent X-radiation which can be detected in the conventional manner; If the material contains several elements, each element is separately excited by primary X-radiation having a wavelength shorter than the absorption edge of that element which causes that element to..emit its characteristic radiation.. For a quantitativedetermination,"the intensity of radiation from the elementinzthe material being analyzed V is'comp'aredwith the intensitytobtaiued in like. manner firom a material oflike composition containing'a'known amount of the element. J

trum'called'the whiteradiationg This white radiation willexcite other elements in lthematerialiwhose absorption g absorption edges lying above the shortest Vwave length of theprimaryX-radiation. fThus, if the secondary radi ator contains only one element which is' excited into fluorescence by the primary X-radiation, 'an intense monochromaticbeam of X-radiation will be produced by-the secondary radiator. is, f I j 1 By choosing a secondary radiator which emitsa' monochromatic beam of X-radiation and exposing the material to that monochromatic X-ray beam, only elements in the material having-an absorption edge lying above the wavelength of the X-rays from the secondary radiator willbe excited into generating their characteristic fluorescent radiation. e V V The secondary radiator may be a solid, liquid, vapor,

or gas; it may be a single element, a mixture of elements;

a compound'or an alloy, since only that element or elements whose absorption edges are higher than the shortest wave-length ofthe primaryX-radiation will emit their characteristic radiation.- If the secondary radiator is a thin foil, or the order of 0.001 inch, maximum amount of fluorescence may be had since greater thicknesses-do 1 not contribute, andthe harder primary radiation may,

' for the most part,

of,or for determining the thickness. of a coating of one f 1 For; most materials; quitei'satisfactory results are ob-" However, for certain -combina;

edges lie at wave-lengths shorter than that of the element v whose presence is being determined and creates dif -V ficulties in resolving the secondary: radiation ir'o'mthe I element by the detection system.

A'principal object of my invention is to provide an improved methodand apparatus for; the "non-de structive analysis of materials by X-rays, V

A further object of my invention is to of materials by X-rays. V I a V A still further object of my invention is to provide a method and apparatus for the non-destructive analysis These and further objects of my invention will appear as the specificationprogresses.

lnaccordance with my invent-ion'I: have'found thatithe Lundesirable "white radiation which will' excite undesired elements in the material. to .fluoresce and emit'their charprovideasimple and dependable apparatus for the non-destructive analysis V baflied away. j I

xMy invention may be used to quantitatively analyze compositions such as ores for constituent elements therecomposition on a base of another composition. I prefer therefore, to employ a detector which willdiscriminate V between'spectral linesof different elements which may I I be present in 'the compositiongiving'rise to the secondary;v T X-raysjfrom the Specimen; For this purpose, I prefer,

to use a' proportional counter I in combination with a pulse-height discriminator as the formenwill provide pulses of height proportional to the energy contentcf I thespect'ral lines. given oif by the elements of thecom- V V position whilefthe ,pulse-height'discriminator can be adjusted to pass pulses withinfa specific range while reject-- ing'others' It is expressly understood, however, that otheritypes, of detectors, such as scintillationcounters, Gciger Miiller counters, ionization chambers and'theflike may be used. Moreover, since there'may be appreciable scattered radiation from the specimen, I'prefer'to employ a filter V or combination of. filters ,between the specimen and thedetectorto eliminate suchscattered'radiation. jIn one embodiment ofmy invention, I analyze zinc; iron-and' lead containingores for zinc content.

ores. frequently contain other impurities such as calcium and magnesiumca'rbonates. By usingagermanium radi-.,

ator, the Ge Ka radiation (1.256 A.) efliciently excites the zinc K levelstk-absorption edge at 1.284 A.) but does 'notexcite-the Pb L-spectrum (edges at .782, .815, and'.950 A.). Fe, Ca, vMg,'and S (if the iron iscombinedfas FeS) are also excited, butthe last two are absorbed in the air-path between the ore specimen and the detector. The Fe and Ca are clearly resolved from the Zn as well as each other using a proportional, counter detector 'and pulse height discriminator. Further spectral V to integrating the spectralcurve.

acteristic X-rays can be eliminated by exposing the ma- V v I ter ial togfluorescent X-raysproduced by a secondary'radiator which is' exposed to theprimary X-radiation. {The secondary radiator will only generateX-rays whichare' by a secondary'radiator containing nickel, copperyzinc.

characteristic of elements contained therein have purity may be achieved by using a copper filter to eliminate 'Ge Km scatter from the specimen and the Zn KB peak. Zn K0: remains isolated when the discriminator V remains properly adjusted with its base line set properly.

The recorded intensity may be increased by adjusting the base line to avoltage on the low amplitude side of the V zinc peakpand opening the window-to-include the entire rangeof zinc radiationpulse heights. This is equivalent,

In another embodiment offmy invention 1 measure the thickness ofja zinc coating on a steelbase by excitingf the latter to fluoresce with secondary 'X-rays produced;

or gallium. The Zn Kat line cannot be excited by the.-

'pass through the radiator and be Such .K line is, however, .partially absorbed bythelzincaand .can be detected byntheflcounter; 'If the intensity.:of-.-the Fe K06 line is measured, i.e. by counting the-number of pulses per time interval obtained-from -the counter, .and compared with the intensity obtained inlike manner from a sample of the same composition but .of

'known coating thickness, the .thickness of theazinc coat- .ing can be determined. a

The invention will be described in connection with "the accompanying drawing showing an apparatus for :measuring the thickness of a zinc coating on a steel,

base.

The particular embodiment of the invention about to be described in connection with the drawing is illustrative only as the invention is not limited to the measurement of zinc coatings on steel. However, asone of the important uses of the invention will be the measurement of the thickness of zinc coatings on steel, it will be described in this connection.

:In the drawing -a steel base 1 covered with azinc coating 2 is exposed to secondary X-rays produced by a secondary radiator 3 consisting of a copper plate. The secondary radiator is excited by .primaryX-rays produced by an X-raytube 4. The primary X-rays generated by the tube -4 must have sufficient energy to excite by fluorescence the Cu KCt lines in .thezsecondary radiator efficiently. The Cu K05 lines, .in turn, are wildciently short in wave-length; to generateFe Kat X-rays in the steel base but are :too long to generate Zn Kcc:

lines in the zinc coating. Although Zn (L)'lines .may be generated they are too soft and are readily absorbed in air. the zinc coating with little absorption thus exciting the base ;into fluorescence with a relatively strong Fe K06 line.

After passing through the coating, the Fe Kaa line is detected by a proportional counter '5. Alternatively, a :scintillation counter and photomultiplier orGeiger- Miiller. counter may be used to detect the 'Fe Km line emergingfmm the coating. Pulses from the proportional counter are amplified linearly by amplifier 6 and passed through a pulse height analyzer 7 adjusted so that on-lypulses corresponding in amplitude to Fe 1(05 radiation are counted by counter 8.

-'Since most of the radiation striking the zinc coated steel consists of Cu Kat radiation, the scattering of this Moreover, the Cu Kat lines readily-pass through into the detector can 'be serious especially if thevdetector cannot resolve the Cu Kc and Fe KOL lines very well. In this event, a cobalt filter 9 may be placed before the detector to suppress Cu KOL lines.

The apparatus described above may also be used for analyzing ores or other materials for the constituent elements thereof. In that case, asample of the material is exposed to the secondary X-rays produced by the radiator 3 which is selected to produce secondary X-rays adapted to excite one of the elements in the specimen. The pulseheightdiscriminator in combination with or without filters is adjusted then to achieve desired spectral purity.

While I have thus described my invention in connection with a particular example, I do not wish to be limited thereto as other embodiments of the invention will be apparent to those skilled in the art without departing from the spiritand scope .of the invention as defined in the appended claims.

What I claim is:

1. Apparatus for measuring the thickness of a zinc coating on a ferrous base comprising a source of polychromatic X-rays, a secondary radiator exposed to said polychromatic X-r-ays consisting of an element selected from the group consisting of nickel, copper, zinc and gallium, means to expose a portion of said zinc coated ferrous base to secondary characteristic X-rays generated by said secondary radiator whereby said ferrous-base is caused to generate. characteristic secondary X-rays, a detector disposed to detectonly the secondary characteristicX-rays generated by said ferrous base after passing through the zinc. coating-and means to measure the intensity of said detected secondary characteristic X-rays.

2. Apparatus as claimed in .claim 1 in which the secondary radiator consists of copper.

3. Apparatus as claimed in claim 2' in which abait filterwis' interposed between the detector and- -the zinc-coated ferrous base. tosuppress Cu Kaa -X-rays.

References Cited in the file of this patent OTHER REFERENCES Re'iifel: Beta-Ray-Excited Low-Energy X-ray Sources,

Nucleonics, March 1955, vol. 13, No. 3, pp. 22 to 24.

UNITED S'IATES PA IENT OFFICE CERTIFICATE OF CORRECTION Patent No.- 2,925,497 February 16, 1960 Irwin I. Bessen It is herebfi certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 41, after "radiat-ion" and before the period insert i.e a polychromatic beam of X-radiation is generated by the tube column 2, line .201 for "orj the": read of the Signed and sealed this 2nd day of August 1960.

(SEAL) Attestz KARL AXLINE' ROBERT c. WATSON Attesti ng Officer Commissioner of Patents 

1. APPARATUS FOR MEASURING THE THICKNESS OF A ZINC COATING ON A FERROUS BASE COMPRISING A SOURCE OF POLYCHROMATIC X-RAYS, A SECONDARY RADIATOR EXPOSED TO SAID POLYCHROMATIC X-RAYS CONSISTING OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF NICKEL, COPPER, ZINC AND GALLIUM, MEANS TO EXPOSE A PORTION OF SAID ZINC COATED FERROUS BAS TO SECONDARY RADIATOR WHEREBY SAID FERROUS BASE BY SAID SECONDARY RADIATOR WHEREBY SAID FERROUS BASE IS CAUSED TO GENERATE CHARACTERISTIC SECONDARY X-RAYS, A DETECTOR DISPOSED TO DETECT ONLY THE SECONDARY CHARACTERISTIC X-RAYS GENERATED BY SAID FERROUS BASE AFTER PASSING THROUGH THE ZINC COATING, AND MEANS TO MEASURE THE INTENSITY OF SAID DETECTED SECONDARY CHARACTERISTIC X-RAYS. 